1. Field of the Invention
The present invention generally relates to a method for controlling UV irradiation for curing a semiconductor substrate and a method for processing a semiconductor substrate using the UV irradiation controlling method.
2. Description of the Related Art
Traditionally, UV processing apparatuses have been commonly used for the modification of various processing targets with UV light and the production of substances by means of photochemical reaction. The recent trend of higher integration of devices results in increasingly finer wiring designs and multi-layer wiring structures, which gives rises to a need to reduce the interlayer volume in order to increase the device speed while reducing the power consumptions. To reduce the interlayer volume, low-k (low dielectric constant film) materials are used. However, use of a low-k material results in lower mechanical strength (indicated by elastic modulus, or EM) as the dielectric constant decreases, which makes it difficult for the low-k material to withstand the stress received in subsequent processes such as CMP, wire bonding and packaging. One method to improve the above problem is to cure the low-k material through UV irradiation and thereby increase its mechanical strength (refer to U.S. Pat. Nos. 6,759,098 and 6,296,909 for examples of this method). When irradiated by UV light, the low-k material shrinks and hardens, resulting in a 50 to 200% increase in its mechanical strength (EM).
Highly integrated devices available in recent years are also forcing the industry to find ways to form various thin films via thermal CVD or PECVD in a condition free from damage or flaw due to heat or plasma. As an approach to address this need, photo CVD involving photochemical reaction has been studied for some time.
When the processing target or reaction space is to be irradiated with optical energy under any photo CVD method, however, the UV lamp must be separated from the reaction space because: (1) the pressure and ambient gas in the reaction space must be controlled, (2) the UV lamp will become dirty due to generated gas, and (3) generated gas must be discharged safely. An optical-transmission type window glass made of synthetic quartz, which transmits optical energy, has generally been used to constitute a partition for separating the two (although many types of glass are available, synthetic quartz has been favored because it is relatively inexpensive and has the ability to transmit various lights over a wide spectrum up to the UV range in a vacuum atmosphere).